Subset reduction

The general rule every pattern above is a special case of.

Every pattern in the lessons before this one is this rule wearing a costume. When one number's covered cells sit entirely inside another's, subtract the smaller from the larger: the difference between their counts tells you about exactly the cells left over. Learn it and you never have to recognise a named pattern again.

Drill 1 of 5

Flag every mine and open every safe cell you can prove.

All drills

How to Play!

  1. 1)Create a room code — it can be anything you want
  2. 2)Share your room code with friends
  3. 3)Play together!

KEYBOARD

Arrows / WASD
Move the cursor
Space / Enter
Reveal a cell
F
Flag a cell
Esc
Hide the cursor
Full rules and chordingWhy these boards never need a guessPattern drillsToday's daily challenge

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